The Fascinating Lives of Frogs

Frogs are quite simply: amazing. With over 4,700 species the world over and more being discovered each year, they are one of the most numerous types of life on earth (1). Humans belong to only one species, Homo sapiens, so its a wonder how frogs have yet to take over. The secret to the frogs success is their ability to adapt to very specific ranges of land or their environmental niche.

Ichthyostega aka the first four legged fish Illustration by Khristine A. Page

The earliest known amphibian, Ichthyostega roamed the earth over 470 million years ago.The modern frog was finished evolving at about 190 million years ago.(2) The first recognizable human ancestor has been traced to about 3 million years ago, so frogs have us beat when it comes to time on earth! This is why there are so many species of frogs. A species is a group of individuals with similar characteristics that are capable of interbreeding and producing offspring that will live to adulthood. With frogs, only the same species is capable of interbreeding and they are usually found in the same environment. Ironically, the frogs specific adaptations can also make it prone to extinction. When these smaller habitats are destroyed naturally or by humans, that species of frog can die out and there will be no more.

What kinds of frogs have developed over millions of years?

With this specific adaptability come the changes to the frog that enables it to live in its habitat. And frogs live everywhere! They are found in the arid deserts of Australia and the freezing temperatures of the Arctic. Frogs live on trees, in ponds, and on land. Due to their highly specialized adaptations, there is no one frog kind that is most populous the world over. The common brown frog is found throughout Europe and north of the Arctic Circle in Scandinavia, the bullfrog is common in North America, and tree frogs are found abundantly in Australia (1).

Tree frog with toe pads

Lifecycle of the frog

Another amazing part of the frogs life is the metamorphosis that they undergo before becoming a fully fledged frog. Frogs and toads lay eggs in still water choosing a good place for hatching. Most tadpoles have a 21 day gestation period. It then hatches and latches onto the nearest plant for support. At this point the tadpole, or polliwog, has a tail for swimming and gills for breathing. A few days later, the tadpole begins to feed itself plants or algae. At five weeks, the tadpole begins to change and grows lungs. Its tail shrinks, legs begin to sprout, and then within two weeks, the frog is fully formed.

Photo by Viridiflavus

Common Frog in mid metamorphosis

Photo by Viridiflavus

Frogs are extremely vulnerable in their egg and tadpole stage. Most frogs are not very involved parents and do nothing more than leave their eggs to hatch. Others, like the poison dart frog, will stand guard over their eggs. The frogs will lay their eggs in a safe place on land If the eggs begin to dry out, the dart frog will urinate on the eggs. When ready, the male dart frogs ,among other species, carry the eggs and tadpoles on their backs or pouches to a water filled plant and place them there for protection. Even though a small water filled plant may be safer from predators, it often has nothing to eat. To stop the tadpoles from eating each other, the female dart frog will lay unfertilized eggs in the plant for the newly hatched polliwogs to eat.

Photo by Christian Fischer

Fun Frog Fact:

The highly endangered Australian midwife frog swallows her fertilized eggs and stops eating. The eggs develop into tadpoles and then she spits them up into a wet area.(3)